Wire-wound electrical resistor



INVENTOR.

BY W ML] Patented Oct. 3 1950 UNITED STATES PATENT OFFICE WIRE-WOUND ELECTRICAL RESISTOR Melvin A. Thom, Brighton, N. Y.

Application June 5, 1948, Serial No. 31,236

3 Claims.

This invention relates to a wire-wound electrical resistor and method of constructing the same, and has for its purpose to afford a construction that will enable the economical and practical manufacture of such resistors where tolerances of from plus or minus one per cent to plus or minus one-tenth of one per cent are demanded.

The conventional practice in manufacturing wire-wound resistors is to determine the resistance by the number of completeturns of Wire, or if the resistance is measured, to fasten the free end of the wire at a single fixed point, which necessarily can cause a variation in resistance as much as results from a complete turn of wire, and consequently it is necessary to discard sometimes as many as fifty per cent or more finished resistors after testing in order to obtain commercial units meeting low tolerance requirements, and it is a particular purpose of the invention to afford a construction and procedure in which re sistors can be manufactured economically in quantities and low tolerances maintained without the usual number of rejects, thus greatly reducing the cost of manufacture and improving the efficiency of the units by producing them more nearly in exact accordance with the required resistance.

Another object of the invention is to afford a structure particularly adaptable to cylindrical porcelain insulating bodies on which the wire is wound, and to provide such hollow porcelain bodies with cylindrical end caps having a plurality of attaching members or lugs distributed or spaced uniformly around the cylindrical porcelain body, thus making it possible to fasten the free end of the wire after winding to an attaching lug selected nearest to the position required for the required resistance and length of wire, thus making it possible to construct a resistor substantially in exact accordance with a definite aresistance'range instead of approximating the required resistance within the ,margin of error of a complete turn of wire as has been the general practice heretofore.

A further purpose of the invention is to afford a resistor having a hollow cylindrical porcelain body on which metal caps are pressed and rigidly attached at the ends with conductors secured to the caps in such a manner that the interior of the porcelain body can be completely sealed and the life of the insulator thus greatly increased.

To these and other ends, the invention consists in the construction and method that will appear clearly from the following description when read in. conjunction with the accompanying drawings, the novel features beingpointed out in the claims following the specification.

In the drawings:

Fig. 1 is a view in side elevation of a resistor constructed in accordance with a preferred embodiment of the invention, and showing the wire wound on a porcelain body and fastened to the attaching lugs, before bending over the lugs;

Fig. 2 is a view similar to Fig. 1, partially in section, and showing the terminal lugs bent back upon the cylindrical bodies of the metal conducting caps;

Fig. 3 is a perspective view of one of the metal conducting caps;

Fig. 4 is a view in end elevation of the same, and

Fig. 5 is a view in side elevation of the same.

Referring more particularly to the drawings in which like reference numerals refer to the same parts throughout the several views, I designates a hollow cylindrical porcelain body or form on which the resistance wire is to be wound, and rigidly fastened to each end of the porcelain body l'is a metal conducting cap including a cylindrical body portion 2 and an end Wall 3 having a central opening therein through which extends a conductor 4 that permits attaching the resistor when it is put in use.

The conductor 4 is provided with an enlargement or head abutting the inner surface of the cap and is rigidly secured against the inner surface surrounding the opening by a silver solder, or in any other suitable manner, whereby the conductor 4 is rigidly fastened to'the end wall 3 of the cap interiorly of the latter. The cylindrical body portion of the cap 2 is provided with the laterally bent attaching members or lugs 5 joined to the cylindrical body by the connecting portions 6 and arranged around the cylindrical body at equal distances or uniformly spaced from each other, and while in the illustrated embodiment there are shown three such attaching lugs, it

is to be understood that the purposes of the invention may be accomplished with two, four, or

more such lugs uniformly spaced around the cy lindrical cap, depending upon the diameter of the porcelain body and the tolerance requirement of the resistors.

Each metal 'cap is also preferably provided in its cylindrical wall with flat areas 1 arranged between the attaching lugs, as shown, making it possible to press the cap on to the cylindrical periphery of the insulating body tightly, by compensating through the flat areas for slight variations in the porcelain due to firing, and thus enabling a uniformly tight and permanent connection between the metal conducting caps and slightly varying sizes of the porcelain body.

After the metal conducting caps are secured to the porcelain body and positioned as shown in Fig. 1, the porcelain body is placed in a conventional winding machine and the wire wound thereon after fastening one end initially to an attaching lug at one end of the porcelain body. As the winding operation is approaching completion, the resistance of a given amount of wire on the resistor can be determined by a sliding contact on the wire connected with a suitable resistance measuring instrument, and when the resistance of a given length of wire is determined to be in accordance with the required resistance of the unit, the Wire is cut and fastened to the attaching lug nearest to the end of the wire to be secured. Where there are three such attaching lugs, the free end of the wire can be secured at any one of the three points spaced uniformly around the periphery of the porcelain body, thus reducing any error to less than one-third of a complete turn around the porcelain body, which in the case of a small diameter resistor is almost negligible.

With this construction of cap and the procedure described above, it is possible to construct a wire-wound resistor with no substantial variation from the required resistance, or having a tolerance of substantially not more than plus or sible to utilize commercially all resistors made according to the invention for such low tolerance requirements, whereas according to previous manufacturing practices, it has been necessary to discard or reject as high as fifty per cent or more of the units in order to come within such low tolerance requiremnents. This has been due to the necessity of approximating a required resistance by determining the number of turns of wire, which is an uncertain factor owing to necessary variations in the diameter of the porcelain body; or by fastening the free end of the Wire, after it is wound, at a fixed point which may vary from the exactly proper point of attachment as much as one complete turn of wire or be characterized by any other variation within one complete turn, while with the present invention according to which the point of attaclnnent can be selected from a series of members spaced uniformly around the porcelain body, it is possible to reduce the difference between the actual resistance and the required resistance to one-third or one-quarter of a complete turn of wire, depending upon the number of attaching lugs formed on the conducting caps.

After the wire is fastened as shown in Fig. 1, all of the attaching lugs 5, including the ones to which the wire is secured by fastening therearound, are bent over on the cylindrical body portions of the caps as illustrated in Fig. 2, after which the entire unit is coated with any suitable insulating and sealing material such as shellac or other plastic, that completely covers and seals the wire winding and also the conducting caps around the conductors 4, which are attachable to any suitable connections when the resistor is placed in operation, and preventing access of moisture to the interior of the porcelain body.

While the invention has been described with reference to the particular construction and method herein shown and described, it is not confined to the precise details disclosed, and this application is intended to cover such modifications or departures as may come within the pur poses of the improvement or the scope of the following claims.

I claim:

1. An electrical resistor comprising a hollow cylindrical porcelain body, a cylindrical cap pressed on each end of the porcelain body and including spaced flat areas in its cylindrical Wall engaging the cylindrical surface of the porcelain body and acting to hold the cap securely thereon, each cap having a conductor extending through a central opening in its end wall and secured to the inner surface of the cap surrounding said opening, a plurality of attaching lugs bent back upon the cylindrical Wall of the cap and arranged at equal distances around the cap, and a length of wire wound on the porcelain body having one end attached to one of the caps and the other end fastened to the selected attaching lug on the other cap which determines the proper length of wire for the required resistance 2. An electrical resistor comprising a hollow cylindrical porcelain body, a cylindrical cupshaped conducting cap pressed over each end of the porcelain body, each cap having spaced flat areas in its cylindrical wall engaging the cylindrical surface of the porcelain body and acting to hold the cap securely thereon, one of the conducting caps, at least, having a plurality of angularly spaced attaching lugs integral therewith and'bent back from its mouth onto the cylindrical wall of the cap and arranged at equal distances around the cap, and a length of wire Wound on the porcelain body and having one end attached to one of the conducting caps and its other end fastened to the selected attaching lug of said plurality of attaching lugs on the other cap which determines the proper length of wire for the required resistance.

3. An electrical resistor comprising a hollow insulating body, a cup-shaped conducting cap secured to each end of the insulating body, each conducting cap having a plurality of angularly spaced attaching lugs integral therewith and bent back from the mouth of the cap onto the side wall of the cap and arranged at equal distances around the cap, and each conducting cap having its bottom wall extending over and closing the adjacent end of the insulating body, a conductor extending through a central opening in the bottom wall of each conducting cap and secured to the inner surface of the cap, and a length of wire wound on the insulating body and having one end attached to the cap at one end of the in sulating body and its other end fastened to the selected attaching lug on the other cap which determines the proper length of wire for the required resistance.

MELVIN A. THOM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Denmark Sept. 3, 1945 

